1. Field of the Invention
The present invention relates to a micro-sample pick-up apparatus used for picking up a micro sample for an electron microscope or the like, the micro sample being cut out with a charged particle beam or the like.
2. Description of the Related Art
Focused ion beam systems are adapted for minute scale processing of an arbitrary area. The focused ion beam systems have been widely used for preparing samples for TEM (Transmission Electron Microscope) observation or the like for detecting wafer defects produced in the course of fabrication of semiconductor devices.
As a method of preparing samples for TEM observation of a particular area of a wafer, there have conventionally been known a method called a pick-up method or a lift-out method (see, for example, Document 1). Description will hereinbelow be made on this method with reference to FIGS. 4A to 4D. First, as shown in FIG. 4A, a focused ion beam 7 is irradiated on a desired area of a wafer 6 for performing a thinning processing on an observation target area. Subsequently, as shown in FIG. 4B, the thinned portion is made to adhere to a tip of a probe 2 so as to be picked up as a micro sample 1. A microscope system equipped with a manipulator, as shown in FIG. 6, is used for picking up the micro sample. The microscope system with manipulator includes the probe 2, a probe holder 3 for holding the probe, an XYZ driver mechanism 5 for operation of the probe, and an optical microscope 11. The micro sample 1 is extremely small, having a transverse dimension of 10 to 20 μm and a longitudinal dimension on the order of 5 μm. Hence, an electrostatic force between the tip of the probe 2 and the micro sample 1 may be utilized for causing the micro sample 1 to adhere to the tip of the probe 2. The micro sample 1 is placed on an organic thin film 9 as shown in FIG. 4C. An article consisting of the micro sample 1 resting on the organic film 9 is committed to TEM observation as an observation sample. Once placed on the organic thin film 9, the thinned sample cannot be processed further. However, in a case where the thin sample thus picked up requires an additional processing (hereinafter, the lift-out method permitting the additional processing is described), the thin sample 1 is placed on a special sample stage 8 in an upright position, as shown in FIG. 4D. In this case, the placement of the micro sample requires an exact positioning. While FIG. 4D depicts the special sample stage 8 in a rectangular shape, the form of the special sample stage is not limited to the rectangular shape and various other shapes ar proposed (see, for example, Document 2).
[Document 1]
F. A. Stevie et al., “Application of focused ion beam lift-out specimen preparation to TEM, SEM, STEM, AES, STEM, AES and SIMS analysis”, Surface and Interface Analysis, 31, pp 345(2001)
[Document 2]
Daisuke, Sakata, “FIB lift-out method permitting additional processing”, the gist of lectures of the 58-th session of Japan Electro-microscopy Society, Vol. 37, p247(2002)
The micro sample to be picked up is made to adhere to the probe by way of the electrostatic force between the probe and the micro sample, so that the micro sample on the probe may be oriented in any direction. Therefore, the probe is rotated in order to orient the micro sample downwardly relative to the probe before the micro sample thus picked up is placed oh the organic film. In the conventional microscope system with manipulator, as well, the probe may be rotated by an operator directly manipulating the probe holder with his hand 10. However, this may lead to a problem that the micro sample may be lost because of vibrations associated with unsteady hand movements (FIG. 5A), or that the sample may be increased in the degree of eccentricity due to displacement caused by the unsteady hand movements (FIG. 5B). Furthermore, the lift-out method permitting the additional processing requires the micro sample to be exactly positioned and besides to be precisely controlled for its orientation when the micro sample is placed on the sample stage in the upright position. Unfortunately, however, the conventional method does not offer the ability to control the orientation of the micro sample with high precisions, thus involving a potential problem of the fall of the micro sample (FIG. 5C).
The foregoing examples have been described with reference to the case where the optical microscope is used as observation means. In a case where an electron microscope or ion microscope is used as the observation means, the probe is disposed in a vacuum apparatus which does not allow for a direct access to the probe holder. Therefore, it is impossible to make adjustment on the micro sample with respect to the rotational direction.
In view of the foregoing, it is an object of the invention to provide a micro-sample pick-up apparatus and method adapted to accomplish a high-precision control of the micro sample with respect to the rotational direction, without applying vibrations to the probe holder.